IBD is not common, though it's normal for any caring snake owner to be a little paranoid about it. It's not clear to me why you'd even be worried about it? How long have you had her? Any other snakes? Did you quarantine her? The "missing feces" wouldn't concern me- snakes don't "go" once per meal anyway, only when they need to, & young snakes eating younger (more digestible) prey often have very little waste leftover, so they hold it until it's worth the effort, ok? (Snakes also conserve water this way.) A snake with IBD is often blatantly uncoordinated- you can google some YouTubes to see what I mean. Not being a perfect gymnast isn't the same thing, LOL. Does sound like you need to fix her humidity though- what substrate are you using? The right one can help a lot, or adding a good-sized "humid hide" with damp moss in it. You also didn't give the cage temps. (highest, lowest, & ambient) & if you're heating this boa like a ball python, it's no wonder she's dehydrated! Boas need a bit cooler temps than BPs. And all your heating devices (including lights if any) NEED to be on a thermostat (preferably) or a dimmer control at the very least. You are HARMING this snake if the cage is routinely too hot...FIX your husbandry. I don't think your snake has IBD, but snakes CAN get neurological damage from being overheated!!! And don't hold a snake by their tail, especially not a heavy-bodied type like a boa. You wouldn't like it either, I promise.